Radiation Embrittlement of Spanish NPP Base Metals and Welds; Mechanistic Interpretation of Available Surveillance Data

The availability of high quality data coming from the Spanish RPV surveillance programme is offering the possibility to verify the applicability of simple semi-mechanistic models and tuning the model parameters. The available sets of surveillance data, of 7 different RPVs, are showing rather consistent behavior confirming that Cu, together with P, is the main responsible for damage due to nano-precipitations. The fluence range is between and 0.84xl018 and 55.6xl018 n cm 2 and the observed transition temperature shifts are always far below admissible limits. Copper ranges between 0.02 to 0.23wtper cent, while Phosphorus variation is between 0.004 to 0.02 lwtpercent. Ni levels are contained and always below 1 wtpercent. The content of Mn are covering a wide range; from 1.13 to 2.07 wtpercent making it possible to analyse its effects. In this paper a mechanistic interpretation of the surveillance data is given showing the possible role of Mn and synergisms of Mn and P/Cu following recent hypothesis that Mn, as well as Ni, are playing a similar basic role in making matrix more sensitive to radiation damage, both for base metals and welds, and enhancing P/Cu effects.JRC.F.4-Nuclear design safet